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While a healthy cactus is beautiful and interesting to look at, one that is suffering from a fungal infection is not. Many different types of fungal pathogens affect cactuses. While cures for fungal diseases for cactuses are few, the ones that are available are natural and organic.

Copper Sulfate Fungicide Mixture

Copper, sulfur and lime are organically approved fungicides for the growing and dormant seasons. Mix 6 1/2 teaspoons of copper sulfate with 3 tablespoons of hydrated lime and 2 pints of water. Filter the mixture through cheesecloth to remove any undissolved particles, and add the liquid to 1 gallon of water and pour the mixture into a garden sprayer. Liberally spray your cactuses with the mixture, repeating every seven to 10 days and whenever it rains. This treatment works for cactuses suffering from Anthracnose and stem rot. Anthracnose is characterized by light brown fungal lesions with pink pustules. Stem rot typically affects younger cactuses, beginning as small yellow spots and turning to brown spores that cause shriveling and shrinkage of the plant.

Removing Diseased Cactuses

Many cactus fungal diseases have no cure, including leaf spot, dry rot and charcoal spot. All three are characterized by discolored circular spots with fruiting bodies that grow as the disease progresses. No fungicides will cure your cactus of these diseases. If your cactus has one of these diseases, the most natural way to control the fungus is to remove and destroy the infected cactus. Always use caution and wear protective clothing, including long sleeves and gloves when removing an infected cactus.

Preventing Fungal Diseases

Fungal pathogens infect cactuses that are weak due to improper growing conditions or care. Providing your cactus with the proper care is a natural preventive to avoid infection. Wet soils are the usual cause for cactus disease and cactuses cannot live in wet or waterlogged soil for long. Make sure your cactuses have soil with excellent drainage. When growing them in a container, choose a specially formulated cactus potting mix and always use a pot with at least one drainage hole. When growing cactuses in the garden, provide a sand mixture amended with 25 percent pumice to provide drainage but also retain nutrients.

Good, Old-Fashioned Water

If you notice fluffy white funguslike bodies on your cactus, this is the sign of a mealybug problem, although you may mistake it for a fungal disease. Also called cochineal insects, mealybugs are small red insects that feed on cactus, producing fluffy white sticky mounds to shield them from the elements as they eat. They're common on prickly pear (Opuntia humifusa), which grows in U.S. Department of Agriculture plant hardiness zones 5 through 10, and related species. You can usually control a small infestation with a strong stream of water from a garden hose. Spray the cactus with water, making sure the stream isn't strong enough to damage the plant. For tough-to-remove mealybugs in hard-to-reach places, use a cup of warm water with 2 drops of unscented dish soap and a soft toothbrush. As always, exercise caution and wear gloves when working around a cactus.